As you use digital audio files, you may find that you have files in formats that aren’t compatible with the software or hardware you’re using. You can convert these files to other formats using a variety of apps, but not every app can handle all formats.
iTunes, for example, supports the following formats: WAV, AIFF, Apple Lossless (ALAC), MP3 and AAC. (It also supports some other formats, such as Audible audiobook formats, but you can’t convert to or from those formats.)
You can convert files using iTunes, but I find that it’s a lot easier to use dedicated apps. On the Mac, the best app, by far, is the free XLD. It can convert to and from a couple dozen audio formats. On Windows, the free version of dBpoweramp offers similar features.
In either of these apps, just choose the output settings you want to use. For example, here are XLD’s settings for converting files to Apple Lossless:
Drag the files onto the app’s icon, or to its window, and click the Convert button. You’ll have files in a new format in a jiffy.
If you use lossless files, remember that you can convert to and from any lossless format – WAV, AIFF, FLAC, Apple Lossless, and others – with no loss of quality. So if you have FLAC files you want to use in iTunes, you can do so by converting them to Apple Lossless. (Note that WAV files don’t support tags very well, so I don’t recommend using them with iTunes. Also, Apple Lossless takes up about half the space, and offers the exact same quality.)
If you have lossy files – MP3 or AAC, for example – you need to know that each conversion you make will degrade the quality slightly. Think of each of these conversions like a photocopy of a photocopy; you probably won’t hear the difference if you convert an MP3 to an AAC once, but if you convert it again, you may have a quality loss.